The present invention relates to a machine tool for machining a workpiece by moving a tool and the workpiece relative to each other and to a pallet changer thereof, and particularly to a machine tool such as a machining center having a pallet changer attached thereto for changing pallets having a workpiece mounted thereon between a table and a pallet stocker, i.e. a pallet loading station and to a pallet changer thereof.
Generally, a machine tool such as a machining center is provided with a pallet changer, by which a pallet having a machined workpiece mounted thereon and placed on the table of the machine tool is exchanged with a pallet having a set-up workpiece mounted thereon and placed on a pallet loading station. Such a pallet changer is disclosed, for example, in Japanese Unexamined Utility Model Publication No. 2-53335. This pallet changer comprises pallet change arms which are adapted to be able to swivel about a vertical axis and to move up and down (in a vertical direction).
The pallet changer for a machine tool disclosed in Japanese Unexamined Utility Model Publication No. 2-53335 is configured of a frame structure including a beam arranged above the pallet change arms, an arm shaft fixed to the pallet change arms and supported vertically movably and swingably by the beam of the frame structure, and actuators arranged on the beam for vertically moving the arm shaft and swiveling it. In exchanging the pallets, the pallets are released from each of the table and the pallet loading station, and the pallet change arms are then moved up through the arm shaft by a first actuator, thereby to lift up the pallets on the table and on the pallet loading station to an upper pallet changing position. Next, the pallet change arms are swiveled through the arm shaft by a second actuator, so that the pallet on the side of the table (i.e. the machining position) is replaced with the pallet on the side of the pallet loading station (i.e. the standby position). After that, the pallet change arms are moved down to a lower pallet mounting position through the arm shaft by the first actuator, and the pallets are placed and fixed on the table and the pallet loading station, respectively.
In the pallet changer for the machine tool disclosed in Japanese Unexamined Utility Model Publication No. 2-53335, the pallet change arms on the sides of both the table and the pallet loading station can be moved down only to the same vertical position along with each other. In other words, the vertical position of the pallet on the side of the pallet loading station is set to the same vertical position as the pallet mounting position on the table.
While the workpiece on the pallet is being machined on the side of the table, the set-up process is conducted, on the side of the pallet loading station, for mounting on a pallet a next workpiece to be machined and removing the machined workpiece from the pallet, etc. In the case of the pallet changer disclosed in Japanese Unexamined Utility Model Publication No. 2-53335, however, the pallet change arms on the sides of the table and the pallet loading station can be moved down only to the same vertical position. Especially in a large-size machine tool such a machining center, this results in the very high vertical position for the pallet loading station, and therefore a stool or the like is required for the set-up job, thereby posing the problem of a deteriorated working environment and safety.
Accordingly, an object of the present invention is to provide a machine tool, and a pallet changer therefor, in which the vertical position of the working surface for the pallet loading station can be set to a lower level than the upper surface of the machine tool table in carrying out the set-up job for changing the pallets between the pallet loading station for set-up job and the table.
Another object of the invention is to provide a machine tool, and a pallet changer therefor, in which the vertical position of the pallet change arm on the side of the pallet loading station can be freely set independently of the vertical position of the upper surface of the table.
According to a first aspect of the present invention, there is provided a machine tool for machining a workpiece by moving a tool and the workpiece in relation to each other, which includes a spindle for mounting the tool thereon, a table for a pallet having the workpiece mounted thereon to be placed on the table, a pallet loading station for conducting the set-up job thereon including the mounting/demounting of the workpiece on/from the pallet, and a pallet changer including a pair of pallet change arms, each pallet change arm having a pallet holder for holding selected one of a pallet on the table and a pallet on the pallet loading station, the pair of the pallet change arms being swiveled about a vertical axis thereby to exchange the pallets between the table and the pallet loading station, the pair of the pallet change arms arranged to be able move independently of each other in the vertical direction.
According to a second aspect of the present invention, there is provided a machine tool for machining a workpiece by moving a tool and the workpiece in relation to each other, which includes a spindle for mounting the tool thereon, a table for a pallet having the workpiece mounted thereon to be placed on the table, a pallet loading station for conducting the set-up job including the mounting/demounting of the workpiece on/from the pallet, and a pallet changer including a support body interposed between the table and the pallet loading station and able to swivel about a vertical axis, and a pair of pallet change arms mounted on the support body and extending horizontally in opposite directions from the support body, the support body being swiveled thereby to move one of the pallet change arms from the side of the table to the side of the pallet loading station and the other pallet change arm from the side of the pallet load station to the side of the table, the pair of the pallet change arms being able to move independently of each other, in the vertical direction, on the support body.
According to a third aspect of the present invention, there is provided a machine tool for machining a workpiece by moving a tool and the workpiece in relation to each other, which includes a spindle for mounting the tool mounted thereon, a table for a pallet having the workpiece mounted thereon to be placed on the table, a pallet loading station for conducting the set-up job thereon including the mounting/demounting of the workpiece on/from the pallet, a base disposed between the table and the pallet loading station, a support body able to swivel in relation to the base about a vertical axis, swiveling means disposed on the base for swiveling the support body, a pair of pallet change arms, each pallet change arm including a pallet holder for holding a pallet on the table or a pallet on the pallet loading station, the pair of the pallet change arms arranged to swivel integrally with the support body by the swiveling means and to be able to move independently of each other in the vertical direction on the support body and first vertical driving means disposed on the support body for vertically moving one of the pair of the pallet change arms, second vertical driving means disposed on the support body in series with the first vertical driving means for vertically moving the pair of the pallet changer arms in cooperation with the first vertical driving means, and a stopper for restricting the movement of one of the pair of the pallet change arms on the side of the table, when the pair of the pallet change arms are moved downward by the second vertical driving means.
According to a fourth aspect of the present invention, there is provided a machine tool for machining a workpiece by moving a tool and the workpiece in relation to each other, which includes a spindle for mounting the tool mounted thereon, a table for a pallet having the workpiece mounted thereon to be placed on the table, a pallet loading station for conducting the set-up job including the mounting/demounting of the workpiece on/from the pallet, a base disposed between the table and the pallet loading station, a support body able to swivel in relation to the base about a vertical axis, swiveling means disposed on the base for swiveling the support body, a pair of pallet change arms, each pallet change arm including a pallet holder for holding a pallet on the table or a pallet on the pallet loading station, the pair of the pallet change arms arranged to swivel integrally with the support body by the swiveling means and to be able to move independently of each other in the vertical direction on the support body, first vertical driving means disposed on the support body for vertically moving one of the pair of the pallet change arms on the side of the pallet loading station, second vertical driving means disposed on the support body in series with the first vertical driving means for vertically moving said one of the pair of the pallet change arms on the side of the pallet loading station in cooperation with the first vertical driving means, and third vertical driving means disposed on the support body in parallel to the first vertical driving means and the second vertical driving means for vertically moving the other of the pair of the pallet change arms on the side of the table.
According to a fifth aspect of the present invention, there is provided a pallet changer which includes a support body able to swivel about a vertical axis and a pair of pallet change arms extending horizontally in opposite directions from the support body, the support body being swiveled thereby to move one of the pair of the pallet change arms from a machining position to a standby position and the other pallet change arm from the standby position to the machining position, wherein the pair of the pallet change arms are arranged to able to move independently of each other in the vertical direction on the support body.
In the pallet changer described above, preferably, during the downward movement of the pair of the pallet change arms, one of the pair of the pallet change arms can further move downward after the other pallet change arm stops. More preferably, the pair of the pallet change arms are moved in the vertical direction by a single operating rod driven by two cylinder units connected in series to each other, so that the pair of the pallet change arms can assume three different vertical positions, and that a stopper restricts the downward movement of one of the pair of the pallet change arms. Further, each of the pair of the pallet change arms may be moved in the vertical direction by a different operating rod driven by a different cylinder unit.
The configuration in which a pair of the pallet change arms can move independently of each other in the vertical direction makes it possible to move each of the pair of the pallet change arms in a different vertical position (height). Thus, one pallet (on the side of the pallet loading station) is not required to be set to the same height as the other pallet (on the side of the table), thereby to allow one pallet (on the side of the table) to be set freely to any height.
Especially, in view of the fact that one of the pair of the pallet change arms can move downward further than the other pallet change arm, the standby position (on the side of the pallet loading station) usable for the setup job, etc. can be set lower than the pallet in the machining position (on the side of the table) facing the machine tool.
Further, the downward movement of one of the pair of the pallet change arms driven by the vertical driving means is restricted by a stopper, so that the other pallet change arm alone can move down further.
Also, by moving the two pallet change arms independently of each other by different vertical driving means, only one of the pallet change arms can be moved downward further than the other pallet change arm.
With the configurations and operations described above, according to the present invention, a pair of pallet change arms are movable independently of each other in the vertical direction, and therefore the vertical position of the pallet change arm on the side of the pallet loading station can be set to a level lower than the vertical position of the pallet change arm on the side of the table of the machine tool. Thus, the working surface of the pallet loading station can be set low, thereby improving the efficiency and safety of the set-up job.